This application is based upon and claims benefit of priority of Japanese Patent Application No. 2002-51545 filed on Feb. 27, 2002, the content of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a method of forming a stator winding of a rotary electric machine.
2. Description of Related Art
A method of electrically connecting ends of plural U-shaped conductor segments by arc-welding has been utilized thitherto. For example, JP-B1-3104700 discloses this kind of method, and a similar method is disclosed also in JP-B2-3196738. Essence of the method disclosed in JP-B1-3104700 is shown in FIGS. 10-13 attached to the present specification.
As shown in FIG. 10, a stator winding is formed by plural U-shaped conductor segments. Four conductors 404 are inserted into a slot formed in a stator core 400, and ends 406 of the conductors 404 extend form one axial end of the stator core 400. The conductor ends 406 make plural pairs of conductor ends as shown in FIG. 11, and each pair of the conductor ends is electrically connected by welding. As shown in FIG. 12, in a welding process, an outside of the pair of conductor ends 406 is restricted by an outside electrode 412, and an inside of the pair of conductor ends 406 is restricted by an inside electrode 410. The outside electrode 412 is formed in a shape shown in FIG. 13. A rod-shaped electrode 414 is placed between the pairs of conductor ends neighboring each other in the circumferential direction.
A torch 420 is brought to a vicinity of the conductor ends 406 which contact the outside and inside electrodes 412, 410 and the rod-shaped electrode 414. A minus voltage is applied to the torch 420 and a plus voltage is applied to the outside and inside electrodes 412, 410. Each pair of conductor ends is welded by heat generated by arc discharge between the torch 420 and the conductor ends 406. All the pairs of conductor ends are welded in this manner one by one by moving the torch 420.
In the conventional welding process described above, however, it has been difficult to establish a close contact between the conductor ends to be welded by restricting them with the outside and inside electrodes 412, 410, because there is a space between two pairs of conductor ends aligned in the radial direction. If the conductor ends 406 to be electrically connected to each other by welding do not closely contact each other, they may not be sufficiently welded.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved method of forming a stator winding, and more particularly to provide a method of forming a good electrical connection between ends of U-shaped conductor segments.
A stator of a rotary electric machine such as an alternator for use in an automotive vehicle is composed of a cylindrical stator core and a stator winding formed in the stator core. The cylindrical stator core has plural slots into which U-shaped conductor segments forming the stator winding are inserted.
In a process of forming the stator winding, the plural U-shaped conductor segments, each having a turning portion and straight portions, are inserted in the slot from one axial end of the stator core. Plural straight portions, e.g., four straight portions, are inserted into one slot, so that ends of conductor segments extend from the other axial end of the stator core. The segment ends extending from the stator core are bent to make plural pairs of segment ends to form the stator winding by electrically connecting the segment ends belonging to each pair.
The plural pairs of the segment ends are positioned along two or more coaxial circumferences. Each pair on one circumference is aligned in a zigzag manner in the radial direction with respect to each pair on the other circumference. In order to correctly position the pairs of segment ends and to establish a close contact between segment ends belonging to each pair, the pairs of segment ends are restricted by a restricting device composed of an inside restricting member and an outside restricting member. Each pair of segment ends is individually interposed between both restricting members and pressed by them.
Then, a welding electrode of a welding apparatus is brought to a vicinity of each pair of segment ends so that the segment ends belonging to each pair are welded by heat generated by an arc-discharge between the welding electrode and the segment ends. In this welding process, the stator is rotated relative to the welding electrode, while maintaining the welding apparatus activated and keeping a predetermined distance between the welding electrode and each pair of segment ends. Thus, all pairs of segment ends are continuously welded one by one, establishing electrical connection between segment ends belonging to each pair. Since the welding apparatus is kept activated during the welding process, the arc-discharge is kept stable, and a time required for the welding process is shortened. In the welding process, the arc-welding may be replaced with other methods such as soldering or ultrasonic welding.
In the process of restricting the pairs of segment ends, it is preferable to use a space-keeping member in addition to the inside and outside restricting members. The space-keeping member is inserted between neighboring pairs of segment ends that are aligned along the circumference to correctly keep a predetermined space between the neighboring pairs. The space-keeping member may be formed integrally with the inside and outside restricting members, or it may be formed separately therefrom.
According to the present invention, pairs of the segment ends are correctly positioned, and segment ends belonging to each pair closely contact each other. Therefore, electrically connection in each pair of segment ends is attained by welding without fail.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.